The invention concerns an electric heating device comprising an electric radiator passed through by the air to be heated and in particular passed through by at least part of an air flow produced by an air flow generator, such as a fan or blower.
The field of application of the invention is more particularly that of heating and/or air-conditioning apparatuses for vehicles, in particular private and commercial motor vehicles and heavy lorries.
Usually, the heating up of the air intended for heating the passenger compartment of a motor vehicle, and for demisting and defrosting, is provided by passing a flow of air through a heat exchanger through which the engine block cooling liquid runs.
This heating method may prove unsuitable or insufficient in a number of situations such as:                preconditioning before starting the engine in order to provide heating up of the passenger compartment, and defrosting or demisting, in a remote or pre-programmed manner, before use of the vehicle in a very cold environment,        desired very fast rise in temperature in the passenger compartment,        inability of the heat exchanger to supply the calories necessary for satisfactory heating up of the air in order to provide the heating functions and possible defrosting and demisting functions, as occurs during a certain time after starting, with certain types of engine with low heat loss.        
To overcome these drawbacks, a known solution, among others, consists of adding to the heat exchanger an electric radiator disposed downstream of the exchanger in the circulation duct for the air to be heated up. The operation of the electric radiator is controlled on a temporary basis, until the heat exchanger on its own can provide the heating of the air in the required manner.
Usually, such a supplementary electric radiator uses resistive elements in the form of positive temperature coefficient (PTC) resistors. The use of PTC resistors in fact allows temperature self-limiting so that excessive heating is avoided. The PTC resistors are in the form of small blocks or “jewels”, disposed in heating bars, between two electrodes. Radiant elements are associated with the bars in order to facilitate heat exchange with the air flow passing through the radiator. These radiant elements can be fins through which the bars pass or else inserts for example in the form of pleated or corrugated metal strips disposed between parallel bars.
The additional PTC resistor electric radiators work satisfactorily but have the drawback of having a high production cost owing to the cost of the PTC resistors, the number of constituent components, the necessary assembly time and the sensitivity to corrosion of the supply electrodes of the PTC resistors.